As a material diffusing heat generated from electronic devices, a graphite-based thermal countermeasure has been used. With the technical advancement in performance of electronic devices, amounts of heat generation therefrom have increased. In order to deal with such increased amounts of heat generation, it is required that the graphite materials are designed to be sufficiently thicker to be capable of releasing larger amounts of heat from the devices.
In conventional arts, a method in which one piece of a thick polymer film is electrically sintered to produce a thick graphite material has been proposed (JP-A-60-181129). Furthermore, there has been a method in which multiple pieces of polymer films are layered, and the layered films are subjected to a heat/pressure treatment to produce a thick graphite material (JP-A-61-2775116).